cid#1606633 Overflowed constant

just return early on this failure

Change-Id: I0f8d1455e5349af0604818db1a519f2147d51f33
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/173380
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolan.mcnamara@collabora.com>

filter/source/graphicfilter/icgm/bitmap.cxx

@@ -325,7 +325,10 @@ bool CGMBitmap::ImplGetDimensions( CGMBitmapDescriptor& rDesc )
         rDesc.mbStatus = false;
 
     if (!rDesc.mnX || !rDesc.mnY)
+    {
         rDesc.mbStatus = false;
+        return false;
+    }
 
     sal_uInt32 nHeaderSize = 2 + 3 * nPrecision + 3 * mpCGM->ImplGetPointSize();